Coal preparation plants separate organic and non-organic solid particles by their specific gravities. The coal preparation plant receives a feed of raw mined coal, and separates the raw mined coal into clean coal and refuse. These plants typically utilize two basic processing methods for separating raw coal from rock and varying proportions of striated rock and coal from the higher quality coal. The two processing methods include heavy media and water based separation methods. Heavy media, utilizing a slurry of media, e.g., water and magnetite or ferrosilicon, to separate the coal from the refuse according to their specific gravity of dry solids, is the most common separation process for larger size (Plus 1 mm-0.5 mm) particles. Whereas, water based separation processes are more commonly used for the “cleaning” of the finer sized particles, as that term is commonly understood in the coal processing art. One type of heavy media circuitry used in the coal preparation plants includes a heavy media cyclone.
Coal preparation plants using heavy media cyclones operate with three separate types of screens for coal processing, namely, a deslime screen, a refuse screen and a clean coal screen. A common screening assembly used in many coal preparation plants today is known as a vibratory banana screen. The deslime screen receives the raw coal feed particles and separates them into coarse and fine sized fractions. The coarse or larger sized particles discharged from the deslime screen surface are directed to the heavy media separation section of the coal preparation plant, while the finer sized particles passing through the deslime screen are directed toward the water based separation section of the coal preparation plant.
The clean coal and refuse screens receive the clean coal and refuse particles, respectively produced by the heavy media separating section. While on the clean coal and refuse screens, the clean coal and refuse particles are rinsed with water, and the finer particles and water passing through the respective screens are recirculated through the coal preparation plant. Rinsing the clean coal and refuse particles is primarily done to recover the particles of media, such as magnetite, remaining thereon as a result of the coal/refuse separation process, as magnetite can be quite expensive.
Traditionally, the majority of the media recovered by the clean coal and refuse screens is recovered as a slurry of media and water in the drain section of the underpan for each of the clean coal and refuse screens. This media is mixed with sized raw coal discharged from the deslime screen, piped to a pulping column and pumped from the pulping column to the heavy media separation section of the coal preparation plant.
The mixing of raw coal and media using conventional pulping columns requires the inclusion of the heavy media sump for the retention of media overflowing from the pulping column upon the addition of the raw coal feed. As raw coal is added to the pulping column, the displacement of media with raw coal increases the level in the pulping column forcing the displaced media into the heavy media sump. Conventional pulping columns may include an overflow which reports to a separate heavy media sump. The displaced media is then pumped back into the system. Alternately, conventional pulping columns may be integral to the heavy media sump to collect the overflow. These systems increase the overall size of the plant footprint, and add to the cost of building the coal preparation plant.
The present invention is directed toward overcoming one or more of the above-mentioned problems.